PROJECT SUMMARY Torque teno viruses [TTV] are small DNA viruses which are part of the virome and establish chronic infections in several mammalian hosts, including humans and domestic and farm animals. A considerably large body of epidemiological evidence indicates that TTV?s are associated with several human disease conditions such as hepatitis, respiratory illness, autoimmune disorders and cancers. TTV?s are also known to contaminate drugs, vaccines and the blood supply. Despite the accumulation of epidemiological evidence, there is currently little information about mechanisms of pathogenesis of TTV?s; possibly because of a lack of reliable in-vitro and in-vivo models to study TTV?s. The long term objectives in this research are to use TTV?s as a model to assess the effects of vaccine contamination with extraneous agents, determine how an individual?s viral microbiome can influence their responses to vaccines and to delineate the role of TTV as a primary and co-infecting pathogen. The objective in this application is to establish patterns of TTV infections and co-infections in a swine model and determine how TTV specific cell mediated and humoral immunity can influence the establishment of infection and host immunity. The central hypothesis is that infection of swine with recombinant TTV replicative viral particles will result in virus dissemination to lymphocytes and major organ systems. The secondary hypothesis is that co-infection of swine with TTV and a swine influenza virus will exacerbate clinical signs of influenza. The rationale for the proposed research is that its successful completion can be expected to significantly enhance the capacity of investigators to determine the contribution of TTV to all aspects of human health. The data generated from this proposal will allow the establishment of a solid baseline for TTV infections/ co-infections and its associated immunity, in a swine model. Guided by strong preliminary data, the proposed hypotheses will be tested by pursuit of three specific aims 1) Establish patterns of tissue invasion, replication and immunity of TTSuV1-RVP in swine. 2) Determine the effect of TTsuV1 infection on swine influenza superinfection, in terms of clinical manifestations, colonization and immune responses. The proposed approach is potentially innovative because it enables comprehensive research methods which would not be possible in humans. The established in-vitro culture system for the virus is also likely the first of its kind. The proposed research is significant because its successful completion can be expected to help to eliminate the critical road blocks in TTV research; namely, the lack of reliable in-vitro and in-vivo models to study TTV infections. It will also lay the ground work for in-depth studies to understand TTV infections; enabling significant outcomes for animal and human health in the long term.